Surface Pro and Surface RTThe Surface Pro is a few days away from retail availability in the US and Microsoft has given a select few a look at the hardware. While at first glance it looks nearly identical to the months old Surface RT, there are a pair of pins on either side of the cover port that Microsoft isn’t currently willing to talk about.The Surface Pro has a few more bells and whistles than the Surface RT, including a DisplayPort and USB 3. Those are immediately clear, and explained in any dive into the Pro’s specifications, but tucked away on the bottom of the tablet PC are four pins that you won’t find on the Surface RT. In fact, you won’t find them on the renders Microsoft provided for the Surface Pro advertising either. If you look at the specs sheet on Microsoft’s website, these pins aren’t mentioned at all.Surface Pro on the left, with two inset connectorsThe extra four pins sit nestled inside the grooves that otherwise exist to allow the Touch Cover/Type Cover lock into place. On the Surface RT the plastic nubs on the covers don’t interact with bottom of the tablet — there are pins for that. The same would would seem to be true for the Surface Pro, until we noticed these two sets of dual connectors while examining the hardware.In order to interact with these pins, the nubs that fit into those grooves need to be roughly three times the size they are now. There’s no reason for the existing covers to use these ports anyway, since they have their own connectors — the six gold pins on the bottom of each device. Furthermore Microsoft has made it clear the covers are interchangeable from the Pro to the RT, and the new covers that were release with the Pro featured only aesthetic changes from the older models.Microsoft didn’t make any mention of these pins until a recent AMA on Reddit, marking the first time these pins were acknowledged. During the AMA, Panos Panay, a member of the Surface team, noted that the pins are an addition to the accessory spine that will allow for high-current transfer between the accessory and the battery.It’s not hard to imagine why Microsoft would want an extra port like this on the bottom of their tablet PC — the pins could be used for an extended battery that clips into place or for a keyboard that includes an extra battery. This design would be similar to a hybrid, like the HP Envy x2, which mates a tablet with a battery-packed keyboard.It could be that Microsoft is waiting to see how successful the Surface Pro is before releasing any additional accessories. This sort of hedging would not be in keeping with Microsoft’s all-out release of the Surface or Windows 8, but they may be cutting their potential losses after weak Surface RT sales.And if that if the case, why not include the pin on the Surface RT? It could be a cost-cutting measure and the fact that the SRT would not benefit from a desktop replacement dock nearly as much as the Pro would, but it would certainly use an external battery for extended on-the-go situations.There is currently no further word from Microsoft but we should know more soon enough — likely by the time the first teardowns land on February 9th.